612 THE PALEONTOLOGY OF MINNESOTA. 



[Technophorus. 



anteriorly, situated in the cavity of the umbonal ridge about midway between the 

 beaks and the posterior extremity of the shell; posterior pedal muscles strongly 

 defined, situated on each side of the cardinal edge and just behind the hinge plate. 

 Pallial line distinct, especially in front and along the base, sinuate posteriorly. 



This fine shell is in no wise related to Clidophorus, to which genus I originally re- 

 ferred the indifferently preserved casts upon which the species was founded. Had I 

 been acquainted with the appearance of casts of the interior of Lyrodesma, which are 

 really very distinctive, it is not likely that I should have been led astray by the slit- 

 like vertical depression in front of the beaks. Compared with other species of the 

 genus, L. major is unusually long posteriorly and narrow without running to an 

 acuminate extremity, the radiating lines on the umbonal ridge are finer and the 

 muscular scars deeper. The species is so distinct that detailed comparisons are 

 scarcely necessary. Still it may be well to say that L. acuminatum and L. cannonense 

 are pointed instead of rounded posteriorly and have much stronger umbonal ridges, 

 while they are also less convex in their basal outlines. 



Formation and locality. A. small valve apparently belonging to this species was found in the Hudson 

 River group near Spring Valley, Minnesota. Casts of the interior are not uncommon near the tops of the 

 hills about Cincinnati, Ohio. These are proportionally a little longer than the geologically higher form of 

 the species which is represented in my cabinet by excellently preserved testiferous examples from the 

 upper beds of the Cincinnati group at Clarksville, Ohio. 



Family TECHNOPHORID^E, Miller. 

 Genus TECHNOPHORUS, Miller. 



Technophorus, MII.I.KK, 1889. North Amer. Geol. and Pal., p. 514. 



Shell small, equivalve, inequilateral, compressed convex, often attenuate and 

 extended posteriorly; anterior end rather short, wider than the posterior, almost reg- 

 ularly roundgd in outline; beaks very small, scarcely, if at all prominent; one or two 

 sharp ridges, with a furrow above each, arise near the beak and extend in a curved 

 direction to the post-basal margin. Anterior part of surface marked with regular 

 concentric lines, generally separated by rows of minute punctae; on the posterior 

 part, especially the cardinal slope, those lines rarely coincide with the margins of 

 the valves, but assume various arbitrary and sometimes ornamental arrangements. 

 Internally a short and thick rib extends downward in each valve from the hinge 

 directly in front of the beaks, while on the posterior side of same a shorter oblique 

 rib, or a mere thickening of the hinge plate, causes the beaks in casts of the interior 

 to appear much more erect and prominent than they do on the exterior of the shell. 

 In casts the beaks of the two valves are not distinguishable but together form a single 

 pyramidal prominence. Anterior adductor scar small, situated immediately in front 

 of the internal rib; posterior scar and pallial line not observed, although most 

 excellent casts were studied. 



